Titanium surfaces characteristics modulate macrophage polarization

The effect of copper content in Ti-Cu alloy with bone regeneration ability on the phenotypic transformation of macrophages

Titanium (Ti) alloys are widely used in bone repair due to their excellent biocompatibility and mechanical properties. However, managing post-implantation inflammatory responses in the defect region and accelerating the healing process remain major challenges in the design of such materials. As a bridge between the innate and adaptive immune systems, macrophages play a pivotal role in bone defect healing through their M2 polarization, which facilitates the secretion of tissue repair-promoting cytokines. Research on the role of copper ions (Cu²⁺) in regulating inflammatory responses at injury sites suggests their potential as active ions for incorporation into alloys as a secondary phase to modulate macrophage polarization. However, the effective concentration and mechanisms in this process remain unclear. Here, we synthesized Ti-xCu (x = 3, 5, 7 wt%) alloys and investigated the effects of copper concentration on macrophage M1/M2 polarization and the underlying mechanisms. In an 8-week rat mandibular bone regeneration experiment, Ti-5Cu demonstrated superior performance compared to pure titanium. At the early stage (2 weeks), Ti-5Cu promoted the dominance of M1 macrophages and upregulated inflammatory cytokines, facilitating the initial inflammatory response. Subsequently, a timely M1-to-M2 phenotype transition was observed, accompanied by elevated expression of the repair-related cytokine IL-10, ultimately leading to improved bone healing. This study provides a theoretical foundation for the development of titanium-copper composite materials with anti-inflammatory and pro-healing properties, paving the way for innovative solutions to promote bone defect repair.

Machine Learning Approach to Investigating Macrophage Polarization on Various Titanium Surface Characteristics

Objective: Current laboratory studies on the effect of biomaterial properties on immune reactions are incomplete and based on a single or a few combination features of the biomaterial design. This study utilizes intelligent prediction models to explore the key features of titanium implant materials in macrophage polarization. Impact Statement: This pilot study provided some insights into the great potential of machine learning in exploring bone immunomodulatory biomaterials. Introduction: Titanium materials are commonly utilized as bone replacement materials to treat missing teeth and bone defects. The immune response caused by implant materials after implantation in the body has a double-edged sword effect on osseointegration. Macrophage polarization has been extensively explored to understand early material-mediated immunomodulation. However, understanding of implant material surface properties and immunoregulations remains limited due to current experimental settings, which are based on trial-by-trial approaches. Artificial intelligence, with its capacity to analyze large datasets, can help explore complex material-cell interactions. Methods: In this study, the effect of titanium surface properties on macrophage polarization was analyzed using intelligent prediction models, including random forest, extreme gradient boosting, and multilayer perceptron. Additionally, data extracted from the newly published literature were further input into the trained models to validate their performance. Results: The analysis identified "cell seeding density", "contact angle", and "roughness" as the most important features regulating interleukin 10 and tumor necrosis factor α secretion. Additionally, the predicted interleukin 10 levels closely matched the experimental results from newly published literature, while the tumor necrosis factor α predictions exhibited consistent trends. Conclusion: The polarization response of macrophages seeded on titanium materials is influenced by multiple factors, and artificial intelligence can assist in extracting the key features of implant materials for immunoregulation.

The impact of biocorrosion and titanium ions release on peri-implantitis

OBJECTIVES

Biofilm accumulation is considered the primary cause of peri-implant inflammation. Still, metallosis caused by an increased concentration of titanium ions at the site of peri-implantitis site cannot be ignored. Whether titanium ions alone or in concert with bacterial biofilm trigger inflammation and bone destruction in peri-implant tissues remains unproven.

MATERIALS AND METHODS

Articles were retrieved from PubMed/Medline, Web of Science. All studies focusing on titanium ions release in peri-implant reactions were included and evaluated.

RESULTS

Titanium implants are considered non-inert and may release titanium ions in the intraoral microenvironment, the most important of which is the acidic environment created by bacterial biofilms. Although the correlation between titanium ion release and the incidence or progression of peri-implantitis is controversial, several studies have confirmed the potential role of titanium ions. Diffusion or entry of titanium ions into the circulation may be a scavenging effect on local titanium ions but can cause systemic adverse effects. However, existing measures are not yet able to balance reducing biocorrosion and maintaining osteogenic results, and the exploration of new materials requires long-term clinical data.

CONCLUSIONS

Titanium ions have potential impacts on peri-implant tissue and systemic circulation. Titanium ions are closely associated with bacterial biofilms in the occurrence and development of periimplantitis. The preventive strategies for the release and action of titanium ions remain to be explored.

CLINICAL RELEVANCE

Our findings may provide the hope of shedding light on the pathogenesis of peri-implantitis and its treatment.

The Intersection between Immune System and Idiopathic Pulmonary Fibrosis-A Concise Review

Idiopathic pulmonary fibrosis (IPF) is marked by progressive alveolar destruction, impaired tissue regeneration, and relentless fibrogenesis, culminating in respiratory failure and death. A diverse array of resident and non-resident cells within the lung contribute to disease pathogenesis. Notably, immune cells, both resident and recruited, respond to cues from sites of lung injury by undergoing phenotypic transitions and producing a wide range of mediators that influence, initiate, or dictate the function, or dysfunction, of key effector cells in IPF pathology, such as alveolar epithelial cells, lung fibroblasts, and capillary endothelial cells. The role of the immune system in IPF has undergone an interesting evolution, oscillating from initial enthusiasm to skepticism, and now to a renewed focus. This shift reflects both the past failures of immune-targeting therapies for IPF and the unprecedented insights into immune cell heterogeneity provided by emerging technologies. In this article, we review the historical evolution of perspectives on the immune system's role in IPF pathogenesis and examine the lessons learned from previous therapeutic failures targeting immune responses. We discuss the major immune cell types implicated in IPF progression, highlighting their phenotypic transitions and mechanisms of action. Finally, we identify key knowledge gaps and propose future directions for research on the immune system in IPF.

Engineered Strategies to Interfere with Macrophage Fate in Myocardial Infarction

Myocardial infarction (MI), a severe cardiovascular condition, is typically triggered by coronary artery disease, resulting in ischemic damage and the subsequent necrosis of the myocardium. Macrophages, known for their remarkable plasticity, are capable of exhibiting a range of phenotypes and functions as they react to diverse stimuli within their local microenvironment. In recent years, there has been an increasing number of studies on the regulation of macrophage behavior based on tissue engineering strategies, and its regulatory mechanisms deserve further investigation. This review first summarizes the effects of key regulatory factors of engineered biomaterials (including bioactive molecules, conductivity, and some microenvironmental factors) on macrophage behavior, then explores specific methods for inducing macrophage behavior through tissue engineering materials to promote myocardial repair, and summarizes the role of macrophage-host cell crosstalk in regulating inflammation, vascularization, and tissue remodeling. Finally, we propose some future challenges in regulating macrophage-material interactions and tailoring personalized biomaterials to guide macrophage phenotypes.

Effect of 3D-Printed Polycaprolactone Scaffold With Powdery/Smooth Micromorphology on Local Immune Environments

Selective laser sintering (SLS) has become a viable approach for producing biodegradable medical implants in various clinical applications. The resulting scaffolds typically exhibit a powdery microstructure, which may potentially impact the behavior of immune cells and immune responses in surrounding tissues. However, limited research has been conducted to understand the effect of surface morphology in SLS-fabricated scaffolds on local immune environments. This study aims to compare the effect of SLS-fabricated polycaprolactone (PCL) scaffolds with powdery and smooth surface morphologies on immune-related biological responses. Compared with those on the powdery micromorphology, RAW264.7 macrophages displayed greater dispersion and adopted a spread and elongated morphology on the scaffolds with smooth surface. The expression levels of arginase-1 and CD206 were found to be upregulated in macrophages adhering to the PCL scaffolds with smooth surface, accompanied by an augmented secretion of anti-inflammatory cytokines TGF-β and IL-10. Conversely, there was a decrease in the secretion of pro-inflammatory cytokines TNF-α and IL-12. When implanted in vivo, the SLS-derived scaffolds were completely covered by host tissues, Withing increased collagen deposition, indicating good histocompatibility. At 1-week post-implantation, there was a significantly higher presence of M2-type macrophages surrounding the scaffold compared to M1 macrophages in both groups. By 3 weeks post-implantation, the overall level of macrophages had decreased in both groups. However, a significant higher level of M1 macrophages were observed in the powdery scaffold group. At the same time, the number of neutrophils around the powder scaffold increased significantly, demonstrating long-term local inflammatory responses. The results suggested that post-treated scaffolds with smooth surfaces can effectively reduce local inflammation, making them more suitable for clinical implantation.

Anodized Ti6Al4V-ELI, electroplated with copper is bactericidal against Staphylococcus aureus and enhances macrophage phagocytosis

Implants aim to restore skeletal dysfunction associated with ageing and trauma, yet infection and ineffective immune responses can lead to failure. This project characterized the microbiological and host cell responses to titanium alloy with or without electroplated metallic copper. Bacterial viability counting and scanning electron microscopy quantified and visualized the direct and indirect bactericidal effects of the Cu-electroplated titanium (Cu-Ep-Ti) against two different Staphylococcus aureus strains. Human THP-1 macrophage adhesion and viability was analyzed, along with phagocytosis. Results showed potent antimicrobial activity alongside promising host-immunomodulatory properties. Direct and indirect exposure to Cu-Ep-Ti produced potent bactericidal effects resulting in 94-100% reductions in bacterial viability at 24 h, with complete eradication in some cases. As expected, cytotoxicity was observed in THP-1 macrophages without media exchange, though when media was exchanged at 8, 24 and 48 h cell viability was equivalent to Control-Ti. Interestingly macrophages adhered to the copper material or grown in the presence of copper ions showed 7-fold increase in phagocytosis of S. aureus bioparticles compared to Control-Ti, suggesting a dual bactericidal and host immunomodulatory mechanism. In conclusion, this Cu-electroplated Ti biomaterial can limit bacterial contamination on the implant surface, whilst simultaneously promoting a beneficial antimicrobial immune response.

Race for the surface between THP-1 macrophages and Staphylococcus aureus on various titanium implants with well-defined topography and wettability

Gristina et al. (1987) suggested that the fate of a biomaterial is decided in a "race for the surface" between pathogens and the host. To gain deeper insight into the mechanisms behind this concept, we investigated the "race for the surface" across three co-culture scenarios with THP-1 macrophages and Staphylococcus aureus (1:1 ratio), varying the order of addition: (i) simultaneous, (ii) macrophages first, and (iii) S. aureus first, on six Ti6Al4V-ELI surfaces modified with specific topographies and wettability. The outcome of the race for the surface was not influenced by these biomaterials but by the chronological introduction of macrophages and S. aureus. When macrophages and S. aureus arrived simultaneously, macrophages won the race, leading to the lowest number of viable S. aureus through rapid phagocytosis and killing. When macrophages arrived and established first, macrophages still prevailed but under greater challenge resulting from the lower bacterial killing efficiency of adherent macrophages and numerous viable intracellular bacteria, supporting the concept of the so-called immunocompromised zone around implants (upregulation of TLR-2 receptor and pro-inflammatory IL-1β). When S. aureus arrived first establishing a biofilm, bacteria won the race, leading to macrophage dysfunction and cell death (upregulation of FcγR and TLR-2 receptors, NF-κB signaling, NOX2 mediated reactive oxygen species), contributing to a persistent biofilm phenotype (upregulation of clfA, icaA, sarA, downregulation of agrA, hld, lukAB) and intracellular survival of S. aureus (lipA upregulation). The clinical implications are bacterial colonization of the implant and persistence of intracellular bacteria in periprosthetic tissues, which can lead to infection chronicity. STATEMENT OF SIGNIFICANCE: Gristina et al. (1987) suggested that the fate of a biomaterial is decided in a "race for the surface" between bacterial pathogens and host cells. There is a lack of in vitro co-culture models and knowledge on macrophage-S. aureus interactions on biomaterial surfaces, and no studies have evaluated the expression of virulence factors in S. aureus biofilms. We have successfully developed co-culture models and molecular panels, and elucidated important cellular and molecular interactions between macrophages and S. aureus on a broad range of titanium biomaterials with well-defined surface topography and wettability. Our findings highlight the critical role of biofilm formation and the chronological order of bacteria or macrophage arrival in determining the fate of the race for the surface.

Development of Zinc-Containing Chitosan/Gelatin Coatings with Immunomodulatory Effect for Soft Tissue Sealing around Dental Implants

BACKGROUND

Soft tissue integration (STI) around dental implant abutments is a prerequisite to prevent bacterial invasion and achieve successful dental implant rehabilitation. However, peri-implant STI is a major challenge after dental abutment placement due to alterations in the immune microenvironment upon surgical dental implant installation.

METHODS

Based on known immunomodulatory effects of zinc, we herein deposited zinc/chitosan/gelatin (Zn/CS/Gel) coatings onto titanium substrates to study their effect on macrophages. First, we exposed macrophages to cell culture media containing different zinc ion (Zn2+) concentrations. Next, we explored the immunomodulatory effect of Zn/CS/Gel coatings prepared via facile electrophoretic deposition (EPD).

RESULTS

We found that Zn2+ effectively altered the secretome by reducing the secretion of pro-inflammatory and enhancing pro-regenerative cytokine secretion, particularly at a Zn2+ supplementation of approximately 37.5 μM. Zn/CS/Gel coatings released Zn2+ in a concentration range which effectively stimulated pro-regenerative macrophage polarization as demonstrated by M2 macrophage polarization. Additionally, the impact of these Zn2+-exposed macrophages on gingival fibroblasts incubated in conditioned medium showed stimulated adhesion, proliferation, and collagen secretion.

CONCLUSION

Our promising results suggest that controlled release of Zn2+ from Zn/CS/Gel coatings could be applied to immunomodulate peri-implant STI, and to enhance dental implant survival.

Surface modification strategies to reinforce the soft tissue seal at transmucosal region of dental implants

Soft tissue seal around the transmucosal region of dental implants is crucial for shielding oral bacterial invasion and guaranteeing the long-term functioning of implants. Compared with the robust periodontal tissue barrier around a natural tooth, the peri-implant mucosa presents a lower bonding efficiency to the transmucosal region of dental implants, due to physiological structural differences. As such, the weaker soft tissue seal around the transmucosal region can be easily broken by oral pathogens, which may stimulate serious inflammatory responses and lead to the development of peri-implant mucositis. Without timely treatment, the curable peri-implant mucositis would evolve into irreversible peri-implantitis, finally causing the failure of implantation. Herein, this review has summarized current surface modification strategies for the transmucosal region of dental implants with improved soft tissue bonding capacities (e.g., improving surface wettability, fabricating micro/nano topographies, altering the surface chemical composition and constructing bioactive coatings). Furthermore, the surfaces with advanced soft tissue bonding abilities can be incorporated with antibacterial properties to prevent infections, and/or with immunomodulatory designs to facilitate the establishment of soft tissue seal. Finally, we proposed future research orientations for developing multifunctional surfaces, thus establishing a firm soft tissue seal at the transmucosal region and achieving the long-term predictability of dental implants.

Unraveling the Immune Web: Advances in SMI Capsular Fibrosis from Molecular Insights to Preclinical Breakthroughs

Breast implant surgery has evolved significantly, yet challenges such as capsular contracture remain a persistent concern. This review presents an in-depth analysis of recent advancements in understanding the immune mechanisms and clinical implications associated with silicone mammary implants (SMIs). The article systematically examines the complex interplay between immune responses and capsular fibrosis, emphasizing the pathophysiological mechanisms of inflammation in the etiology of this fibrotic response. It discusses innovations in biomaterial science, including the development of novel anti-biofilm coatings and immunomodulatory surfaces designed to enhance implant integration and minimize complications. Emphasis is placed on personalized risk assessment strategies, leveraging molecular insights to tailor interventions and improve patient outcomes. Emerging therapeutic targets, advancements in surgical techniques, and the refinement of post-operative care are also explored. Despite notable progress, challenges such as the variability in immune responses, the long-term efficacy of new interventions, and ethical considerations remain. Future research directions are identified, focusing on personalized medicine, advanced biomaterials, and bridging preclinical findings with clinical applications. As we advance from bench to bedside, this review illuminates the path forward, where interdisciplinary collaboration and continued inquiry weave together to enhance the art and science of breast implant surgery, transforming patient care into a realm of precision and excellence.

The influence of biophysical niche on tumor-associated macrophages in liver cancer

HCC, the most common type of primary liver cancer, is a leading cause of cancer-related mortality worldwide. Although the advancement of immunotherapies by immune checkpoint inhibitors (ICIs) that target programmed cell death 1 or programmed cell death 1-ligand 1 has revolutionized the treatment for HCC, the majority is still not beneficial. Accumulating evidence has pointed out that the potent immunosuppressive tumor microenvironment in HCC poses a great challenge to ICI therapeutic efficacy. As a key component in tumor microenvironment, tumor-associated macrophages (TAMs) play vital roles in HCC development, progression, and ICI low responsiveness. Mechanistically, TAM can promote cancer invasion and metastasis, angiogenesis, epithelial-mesenchymal transition, maintenance of stemness, and most importantly, immunosuppression. Targeting TAMs, therefore, represents an opportunity to enhance the ICI therapeutic efficacy in patients with HCC. While previous research has primarily focused on biochemical cues influencing macrophages, emerging evidence highlights the critical role of biophysical signals, such as substrate stiffness, topography, and external forces. In this review, we summarize the influence of biophysical characteristics within the tumor microenvironment that regulate the phenotype and function of TAMs in HCC pathogenesis and progression. We also explore the possible mechanisms and discuss the potential of manipulating biophysical cues in regulating TAM for HCC therapy. By gaining a deeper understanding of how macrophages sense and respond to mechanical forces, we may potentially usher in a path toward a curative approach for combinatory cancer immunotherapies.

Innate immune regulation in dental implant osseointegration

PURPOSE

Dental implant osseointegration comprises two types of bone formation-contact and distance osteogenesis-which result in bone formation originating from the implant surface or bone edges, respectively. The physicochemical properties of the implant surface regulate initial contact osteogenesis by directly tuning the osteoprogenitor cells in the peri-implant environment. However, whether these implant surface properties can regulate osteoprogenitor cells distant from the implant remains unclear. Innate immune cells, including neutrophils and macrophages, govern bone metabolism, suggesting their involvement in osseointegration and distance osteogenesis. This narrative review discusses the role of innate immunity in osseointegration and the effects of implant surface properties on distant osteogenesis, focusing on innate immune regulation.

STUDY SELECTION

The role of innate immunity in bone formation and the effects of implant surface properties on innate immune function were reviewed based on clinical, animal, and in vitro studies.

RESULTS

Neutrophils and macrophages are responsible for bone formation during osseointegration, via inflammatory mediators. The microroughness and hydrophilic status of titanium implants have the potential to alleviate this inflammatory response of neutrophils, and induce an anti-inflammatory response in macrophages, to tune both contact and distance osteogenesis through the activation of osteoblasts. Thus, the surface micro-roughness and hydrophilicity of implants can regulate the function of distant osteoprogenitor cells through innate immune cells.

CONCLUSIONS

Surface modification of implants aimed at regulating innate immunity may be useful in promoting further osteogenesis and overcoming the limitations encountered in severe situations, such as early loading protocol application.

Immunomodulatory Biomaterials: Tailoring Surface Properties to Mitigate Foreign Body Reaction and Enhance Tissue Regeneration

The immune cells have demonstrated the ability to promote tissue repair by removing debris, breaking down the extracellular matrix, and regulating cytokine secretion profile. If the behavior of immune cells is not well directed, chronic inflammation and foreign body reaction (FBR) will lead to scar formation and loss of biomaterial functionality. The immunologic response toward tissue repair or chronic inflammation after injury and implantation can be modulated by manipulating the surface properties of biomaterials. Tailoring surface properties of biomaterials enables the regulation of immune cell fate such as adhesion, proliferation, recruitment, polarization, and cytokine secretion profile. This review begins with an overview of the role of immune cells in tissue healing and their interactions with biomaterials. It then discusses how the surface properties of biomaterials influence immune cell behavior. The core focus is reviewing surface modification methods to create innovative materials that reduce foreign body reactions and enhance tissue repair and regeneration by modulating immune cell activities. The review concludes with insights into future advancements in surface modification techniques and the associated challenges.

Electrospun Fiber Surface Roughness Modulates Human Monocyte-Derived Macrophage Phenotype

Injuries to fibrous connective tissues have very little capacity for self-renewal and exhibit poor healing after injury. Phenotypic shifts in macrophages play a vital role in mediating the healing response, creating an opportunity to design immunomodulatory biomaterials which control macrophage polarization and promote regeneration. In this study, electrospun poly(-caprolactone) fibers with increasing surface roughness (SR) were produced by increasing relative humidity and inducing vapor-induced phase separation during the electrospinning process. The impact of surface roughness on macrophage phenotype was assessed using human monocyte-derived macrophages in vitro and in vivo using B6.Cg-Tg(Csf1r-EGFP)1Hume/J (MacGreen) mice. In vitro experiments showed that macrophages cultured on mesh with increasing SR exhibited decreased release of both pro- and anti-inflammatory cytokines potentially driven by increased protein adsorption and biophysical impacts on the cells. Further, increasing SR led to an increase in the expression of the pro-regenerative cell surface marker CD206 relative to the pro-inflammatory marker CD80. Mesh with increasing SR were implanted subcutaneously in MacGreen mice, again showing an increase in the ratio of cells expressing CD206 to those expressing CD80 visualized by immunofluorescence. SR on implanted biomaterials is sufficient to drive macrophage polarization, demonstrating a simple feature to include in biomaterial design to control innate immunity.

[Preparation and Performance of a Novel Polyurethane Microporous Film on Polypropylene Medical Mesh Surface]

Objective

This study aims to develop a medical patch surface material featuring a microporous polyurethane (PU) membrane and to assess the material's properties and biological performance. The goal is to enhance the clinical applicability of pelvic floor repair patch materials.

Methods

PU films with a microporous surface were prepared using PU prepolymer foaming technology. The films were produced by optimizing the PU prepolymer isocyanate index (R value) and the relative humidity (RH) of the foaming environment. The surface morphology of the PU microporous films was observed by scanning electron microscopy, and the chemical properties of the PU microporous films, including hydrophilicity, were analyzed using infrared spectroscopy, Raman spectroscopy, and water contact angle measurements. In vitro evaluations included testing the effects of PU microporous film extracts on the proliferation of L929 mouse fibroblasts and observing the adhesion and morphology of these fibroblasts. Additionally, the effect of the PU microporous films on RAW264.7 mouse macrophages was studied. Immune response and tissue regeneration were assessed in vivo using Sprague Dawley (SD) rats.

Results

The PU films exhibited a well-defined and uniform microporous structure when the R value of PU prepolymer=1.5 and the foaming environment RH=70%. The chemical structure of the PU microporous films was not significantly altered compared to the PU films, with a significantly lower water contact angle ([55.7±1.5]° ) compared to PU films ([69.5±1.7]° ) and polypropylene (PP) ([ 104.3±2.5]°), indicating superior hydrophilicity. The extracts from PU microporous films demonstrated good in vitro biocompatibility, promoting the proliferation of L929 mouse fibroblasts. The surface morphology of the PU microporous films facilitated fibroblast adhesion and spreading. The films also inhibited the secretion of tumor necrosis factor-α (TNF-α) and interleukin (IL)-1β by RAW264.7 macrophages while enhancing IL-10 and IL-4 secretion. Compared to 24 hours, after 72 hours of culture, the expression levels of TNF-α and IL-1β were reduced in both the PU film and PU microporous film groups and were significantly lower than those in the PP film group (P<0.05), with the most notable decreases observed in the PU microporous film group. IL-10 and IL-4 levels increased significantly in the PU microporous film group, surpassing those in the PP film group (P<0.01), with the most pronounced increase in IL-4. The PU microporous film induced mild inflammation with no significant fibrous capsule formation in vivo. After 60 days of implantation, the film partially degraded, showing extensive collagen fiber growth and muscle formation in its central region.

Conclusion

The PU microporous film exhibits good hydrophilicity and biocompatibility. Its surface morphology enhances cell adhesion, regulates the function of RAW264.7 macrophages, and promotes tissue repair, offering new insights for the design of pelvic floor repair and reconstruction patch materials.

Modulating the immune system towards a functional chronic wound healing: A biomaterials and Nanomedicine perspective

Chronic non-healing wounds persist as a substantial burden for healthcare systems, influenced by factors such as aging, diabetes, and obesity. In contrast to the traditionally pro-regenerative emphasis of therapies, the recognition of the immune system integral role in wound healing has significantly grown, instigating an approach shift towards immunological processes. Thus, this review explores the wound healing process, highlighting the engagement of the immune system, and delving into the behaviors of innate and adaptive immune cells in chronic wound scenarios. Moreover, the article investigates biomaterial-based strategies for the modulation of the immune system, elucidating how the adjustment of their physicochemical properties or their synergistic combination with other agents such as drugs, proteins or mesenchymal stromal cells can effectively modulate the behaviors of different immune cells. Finally this review explores various strategies based on synthetic and biological nanostructures, including extracellular vesicles, to finely tune the immune system as natural immunomodulators or therapeutic nanocarriers with promising biophysical properties.

Functional Oxidized Hyaluronic Acid Cross-Linked Decellularized Heart Valves for Improved Immunomodulation, Anti-Calcification, and Recellularization

Tissue engineering heart valves (TEHVs) are expected to address the limitations of mechanical and bioprosthetic valves used in clinical practice. Decellularized heart valve (DHV) is an important scaffold of TEHVs due to its natural three-dimensional structure and bioactive extracellular matrix, but its mechanical properties and hemocompatibility are impaired. In this study, DHV is cross-linked with three different molecular weights of oxidized hyaluronic acid (OHA) by a Schiff base reaction and presented enhanced stability and hemocompatibility, which could be mediated by the molecular weight of OHA. Notably, DHV cross-linked with middle- and high-molecular-weight OHA could drive the macrophage polarization toward the M2 phenotype in vitro. Moreover, DHV cross-linked with middle-molecular-weight OHA scaffolds are further modified with RGD-PHSRN peptide (RPF-OHA/DHV) to block the residual aldehyde groups of the unreacted OHA. The results show that RPF-OHA/DHV not only exhibits anti-calcification properties, but also facilitates endothelial cell adhesion and proliferation in vitro. Furthermore, RPF-OHA/DHV shows excellent performance under an in vivo hemodynamic environment with favorable recellularization and immune regulation without calcification. The optimistic results demonstrate that OHA with different molecular weights has different cross-linking effects on DHV and that RPF-OHA/DHV scaffold with enhanced immune regulation, anti-calcification, and recellularization properties for clinical transformation.

Modeling mechanical activation of macrophages during pulmonary fibrogenesis for targeted anti-fibrosis therapy

Pulmonary fibrosis is an often fatal lung disease. Immune cells such as macrophages were shown to accumulate in the fibrotic lung, but their contribution to the fibrosis development is unclear. To recapitulate the involvement of macrophages in the development of pulmonary fibrosis, we developed a fibrotic microtissue model with cocultured human macrophages and fibroblasts. We show that profibrotic macrophages seeded on topographically controlled stromal tissues became mechanically activated. The resulting co-alignment of macrophages, collagen fibers, and fibroblasts promoted widespread fibrogenesis in micro-engineered lung tissues. Anti-fibrosis treatment using pirfenidone disrupts the polarization and mechanical activation of profibrotic macrophages, leading to fibrosis inhibition. Pirfenidone inhibits the mechanical activation of macrophages by suppressing integrin αMβ2 and Rho-associated kinase 2. These results demonstrate a potential pulmonary fibrogenesis mechanism at the tissue level contributed by macrophages. The cocultured microtissue model is a powerful tool to study the immune-stromal cell interactions and the anti-fibrosis drug mechanism.

Electrophoretically deposited titanium and its alloys in biomedical engineering: Recent progress and remaining challenges

Over the past decade, titanium implants have gained popularity as the number of performed implantation operations has significantly increased. There are a number of methods for modifying the surface of biomaterials, which are aimed at extending the life of titanium implants. The developments in this field in recent years have required a comprehensive discussion of all the properties of electrophoretically deposited coatings on titanium and its alloys, taking into account their bioactivity. The development that took place in this field in recent years required a comprehensive discussion of all the properties of coatings electrophoretically deposited on titanium and its alloys, with particular emphasis on their bioactivity. Herein, we attempt to assess the influence of the electrophoretic deposition (EPD) process parameters on these coatings' biological and mechanical properties. Particular attention has been addressed to the in-vitro and in-vivo studies conducted hitherto. We have seen an increased interest in using titanium alloys without the addition of toxic compounds and gaps in the EPD field such as the uncommon endeavors to develop a "Design of experiments" approach as well as the lack of assessment of the surface free energy and detailed topography of electrophoretically deposited coatings. The exact correlation of coating properties with EPD process parameters still seems explicitly not understood, necessitating more future investigations. Ipso facto, the exact mechanism of particle agglomeration and Hamaker's law need to be fathomable.

Biomimetic HA-GO implant coating for enhanced osseointegration via macrophage M2 polarization-induced osteo-immunomodulation

The pro-inflammatory/anti-inflammatory polarized phenotypes of macrophages (M1/M2) can be used to predict the success of implant integration. Hence, activating and inducing the transformation of immunocytes that promote tissue repair appears to be a highly promising strategy for facilitating osteo-anagenesis. In a previous study, titanium implants were coated with a graphene oxide-hydroxyapatite (GO-HA) nanocomposite via electrophoretic deposition, and the osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) was found to be significantly enhanced when the GO content was 2wt%. However, the effectiveness of the GO-HA nanocomposite coating in modifying the in vivo immune microenvironment still remains unclear. In this study, the effects of GO-HA coatings on osteogenesis were investigated based on the GO-HA-mediated immune regulation of macrophages. The HA-2wt%GO nanocomposite coatings exhibited good biocompatibility and favored M2 macrophage polarization. Meanwhile, they could also significantly upregulate IL-10 (anti-inflammatory factor) expression and downregulate TNF-α (pro-inflammatory factor) expression. Additionally, the microenvironment, which was established by M2 macrophages, favored the osteogenesis of BMSCs both in vivo and in vitro. These findings show that the GO-HA nanocomposite coating is a promising surface-modification material. Hence, this study provides a reference for the development of next-generation osteoimmunomodulatory biomaterials.

Material matters: exploring the interplay between natural biomaterials and host immune system

Biomaterials are widely used for various medical purposes, for instance, implants, tissue engineering, medical devices, and drug delivery systems. Natural biomaterials can be obtained from proteins, carbohydrates, and cell-specific sources. However, when these biomaterials are introduced into the body, they trigger an immune response which may lead to rejection and failure of the implanted device or tissue. The immune system recognizes natural biomaterials as foreign substances and triggers the activation of several immune cells, for instance, macrophages, dendritic cells, and T cells. These cells release pro-inflammatory cytokines and chemokines, which recruit other immune cells to the implantation site. The activation of the immune system can lead to an inflammatory response, which can be beneficial or detrimental, depending on the type of natural biomaterial and the extent of the immune response. These biomaterials can also influence the immune response by modulating the behavior of immune cells. For example, biomaterials with specific surface properties, such as charge and hydrophobicity, can affect the activation and differentiation of immune cells. Additionally, biomaterials can be engineered to release immunomodulatory factors, such as anti-inflammatory cytokines, to promote a tolerogenic immune response. In conclusion, the interaction between biomaterials and the body's immune system is an intricate procedure with potential consequences for the effectiveness of therapeutics and medical devices. A better understanding of this interplay can help to design biomaterials that promote favorable immune responses and minimize adverse reactions.

Drug-loaded mucoadhesive microneedle patch for the treatment of oral submucous fibrosis

Oral submucous fibrosis is a chronic, inflammatory and potentially malignant oral disease. Local delivery of triamcinolone to lesion site is a commonly used therapy. The existing methods for local drug delivery include topical administration and submucosal injection. However, in the wet and dynamic oral microenvironment, these methods have drawbacks such as limited drug delivery efficiency and injection pain. Therefore, it is urgently needed to develop an alternative local drug delivery system with high efficiency and painlessness. Inspired by the structure of band-aid, this study proposed a novel double-layered mucoadhesive microneedle patch for transmucosal drug delivery. The patch consisted of a mucoadhesive silk fibroin/tannic acid top-layer and a silk fibroin microneedle under-layer. When applying the annealing condition for the medium content of β-sheets of silk fibroin, the microneedles in under-layer displayed both superior morphology and mechanical property. The mechanical strength of per needle (0.071N) was sufficient to penetrate the oral mucosa. Sequentially, the gelation efficiency of silk fibroin and tannic acid in top-layer was maximized as the weight ratio of tannic acid to silk fibroin reached 5:1. Moreover, in vitro results demonstrated the double-layered patch possessed undetectable cytotoxicity. The sustained release of triamcinolone was observed from the double-layered patch for at least 7 days. Furthermore, compared with other commercial buccal patches, the double-layered patch exhibited an enhanced wet adhesion strength of 37.74 kPa. In addition, ex vivo mucosal tissue penetration experiment confirmed that the double-layered patch could reach the lamina propria, ensuring effective drug delivery to the lesion site of oral submucous fibrosis. These results illustrate the promising potential of the drug-loaded mucoadhesive microneedle patch for the treatment of oral submucous fibrosis.

Modeling Mechanical Activation of Macrophages During Pulmonary Fibrogenesis for Targeted Anti-Fibrosis Therapy

Pulmonary fibrosis, as seen in idiopathic pulmonary fibrosis (IPF) and COVID-induced pulmonary fibrosis, is an often-fatal lung disease. Increased numbers of immune cells such as macrophages were shown to accumulate in the fibrotic lung, but it is unclear how they contribute to the development of fibrosis. To recapitulate the macrophage mechanical activation in the fibrotic lung tissue microenvironment, we developed a fibrotic microtissue model with cocultured human macrophages and fibroblasts. We show that profibrotic macrophages seeded on topographically controlled stromal tissue constructs become mechanically activated. The resulting co-alignment of macrophages, collagen fibers and fibroblasts promote widespread fibrogenesis in micro-engineered lung tissues. Anti-fibrosis treatment using pirfenidone disrupts the polarization and mechanical activation of profibrotic macrophages, leading to fibrosis inhibition. Pirfenidone inhibits the mechanical activation of macrophages by suppressing integrin αMβ2 (CD11b/CD18) and Rho-associated kinase 2, which is a previously unknown mechanism of action of the drug. Together, these results demonstrate a potential pulmonary fibrogenesis mechanism at the tissue level contributed by mechanically activated macrophages. We propose the coculture, force-sensing microtissue model as a powerful tool to study the complex immune-stromal cell interactions and the mechanism of action of anti-fibrosis drugs.

Chitosan-Based Membranes as Gentamicin Carriers for Biomedical Applications-Influence of Chitosan Molecular Weight

Over the past decade, much attention has been paid to chitosan as a potential drug carrier because of its non-toxicity, biocompatibility, biodegradability and antibacterial properties. The effect of various chitosan characteristics on its ability to carry different antibiotics is discussed in the literature. In this work, we evaluated the influence of the different molecular weights of this polymer on its potential as an antibacterial membrane after adding gentamicin (1% w/w). Three types of chitosan membranes without and with antibiotic were prepared using a solvent casting process. Their microstructures were analyzed with a 4K digital microscope, and their chemical bonds were studied using FTIR spectroscopy. Furthermore, cytocompatibility on human osteoblasts and fibroblasts as well as antibacterial activity against Staphylococcus aureus (S. aureus.) and Escherichia coli (E. coli) were assessed. We observed that the membrane prepared from medium-molecular-weight chitosan exhibited the highest contact angle (≈85°) and roughness (10.96 ± 0.21 µm) values, and its antibacterial activity was unfavorable. The maximum tensile strength and Young's modulus of membranes improved and elongation decreased with an increase in the molecular weight of chitosan. Membranes prepared with high-molecular-weight chitosan possessed the best antibacterial activity, but mainly against S. aureus. For E. coli, is not advisable to add gentamicin to the chitosan membrane, or it is suggested to deplete its content. None of the fabricated membranes exhibited a full cytotoxic effect on osteoblastic and fibroblast cells. Based on our results, the most favorable membrane as a gentamicin carrier was obtained from high-molecular-weight chitosan.

Osteogenic and anti-inflammatory effects of SLA titanium substrates doped with chitosan-stabilized selenium nanoparticles via a covalent coupling strategy

Osseointegration is a prerequisite for the function of dental implants, and macrophage-dominated immune responses triggered by implantation determine the outcome of ultimate bone healing mediated by osteogenic cells. The present study aimed to develop a modified titanium (Ti) surface by covalently immobilizing chitosan-stabilized selenium nanoparticles (CS-SeNPs) to sandblasted, large grit, and acid-etched (SLA) Ti substrates and further explore its surface characteristics as well as osteogenic and anti-inflammatory activities in vitro. CS-SeNPs were successfully prepared by chemical synthesis and characterized their morphology, elemental composition, particle size, and Zeta potential. Subsequently, three different concentrations of CS-SeNPs were loaded to SLA Ti substrates (Ti-Se1, Ti-Se5, and Ti-Se10) using a covalent coupling strategy, and the SLA Ti surface (Ti-SLA) was used as a control. Scanning electron microscopy images revealed different amounts of CS-SeNPs, and the roughness and wettability of Ti surfaces were less susceptible to Ti substrate pretreatment and CS-SeNP immobilization. Besides, X-ray photoelectron spectroscopy analysis showed that CS-SeNPs were successfully anchored to Ti surfaces. The results of in vitro study showed that the four as-prepared Ti surfaces exhibited good biocompatibility, with Ti-Se1 and Ti-Se5 groups showing enhanced adhesion and differentiation of MC3T3-E1 cells compared with the Ti-SLA group. In addition, Ti-Se1, Ti-Se5, and Ti-Se10 surfaces modulated the secretion of pro-/anti-inflammatory cytokines by inhibiting the nuclear factor kappa B pathway in Raw 264.7 cells. In conclusion, doping SLA Ti substrates with a modest amount of CS-SeNPs (1-5 mM) may be a promising strategy to improve the osteogenic and anti-inflammatory activities of Ti implants.

Inflammation Responses to Bone Scaffolds under Mechanical Stimuli in Bone Regeneration

Physical stimuli play an important role in one tissue engineering. Mechanical stimuli, such as ultrasound with cyclic loading, are widely used to promote bone osteogenesis; however, the inflammatory response under physical stimuli has not been well studied. In this paper, the signaling pathways related to inflammatory responses in bone tissue engineering are evaluated, and the application of physical stimulation to promote osteogenesis and its related mechanisms are reviewed in detail; in particular, how physical stimulation alleviates inflammatory responses during transplantation when employing a bone scaffolding strategy is discussed. It is concluded that physical stimulation (e.g., ultrasound and cyclic stress) helps to promote osteogenesis while reducing the inflammatory response. In addition, apart from 2D cell culture, more consideration should be given to the mechanical stimuli applied to 3D scaffolds and the effects of different force moduli while evaluating inflammatory responses. This will facilitate the application of physiotherapy in bone tissue engineering.

Osseointegration of Titanium Implants in a Botox-Induced Muscle Paralysis Rat Model Is Sensitive to Surface Topography and Semaphorin 3A Treatment

Reduced skeletal loading associated with many conditions, such as neuromuscular injuries, can lead to bone fragility and may threaten the success of implant therapy. Our group has developed a botulinum toxin A (botox) injection model to imitate disease-reduced skeletal loading and reported that botox dramatically impaired the bone formation and osseointegration of titanium implants. Semaphorin 3A (sema3A) is an osteoprotective factor that increases bone formation and inhibits bone resorption, indicating its potential therapeutic role in improving osseointegration in vivo. We first evaluated the sema3A effect on whole bone morphology following botox injections by delivering sema3A via injection. We then evaluated the sema3A effect on the osseointegration of titanium implants with two different surface topographies by delivering sema3A to cortical bone defect sites prepared for implant insertion and above the implants after insertion using a copper-free click hydrogel that polymerizes rapidly in situ. Implants had hydrophobic smooth surfaces (PT) or multiscale biomimetic micro/nano topography (SLAnano). Sema3A rescued the botox-impaired bone formation. Furthermore, biomimetic Ti implants improved the bone-to-implant contact (BIC) and mechanical properties of the integrated bone in the botox-treated rats, which sema3A enhanced. This study demonstrated the value of biomimetic approaches combining multiscale topography and biologics in improving the clinical outcomes of implant therapy.

Biomaterial scaffolds regulate macrophage activity to accelerate bone regeneration

Bones are important for maintaining motor function and providing support for internal organs. Bone diseases can impose a heavy burden on individuals and society. Although bone has a certain ability to repair itself, it is often difficult to repair itself alone when faced with critical-sized defects, such as severe trauma, surgery, or tumors. There is still a heavy reliance on metal implants and autologous or allogeneic bone grafts for bone defects that are difficult to self-heal. However, these grafts still have problems that are difficult to circumvent, such as metal implants that may require secondary surgical removal, lack of bone graft donors, and immune rejection. The rapid advance in tissue engineering and a better comprehension of the physiological mechanisms of bone regeneration have led to a new focus on promoting endogenous bone self-regeneration through the use of biomaterials as the medium. Although bone regeneration involves a variety of cells and signaling factors, and these complex signaling pathways and mechanisms of interaction have not been fully understood, macrophages undoubtedly play an essential role in bone regeneration. This review summarizes the design strategies that need to be considered for biomaterials to regulate macrophage function in bone regeneration. Subsequently, this review provides an overview of therapeutic strategies for biomaterials to intervene in all stages of bone regeneration by regulating macrophages.

Understanding How Cells Probe the World: A Preliminary Step towards Modeling Cell Behavior?

Cell biologists have long aimed at quantitatively modeling cell function. Recently, the outstanding progress of high-throughput measurement methods and data processing tools has made this a realistic goal. The aim of this paper is twofold: First, to suggest that, while much progress has been done in modeling cell states and transitions, current accounts of environmental cues driving these transitions remain insufficient. There is a need to provide an integrated view of the biochemical, topographical and mechanical information processed by cells to take decisions. It might be rewarding in the near future to try to connect cell environmental cues to physiologically relevant outcomes rather than modeling relationships between these cues and internal signaling networks. The second aim of this paper is to review exogenous signals that are sensed by living cells and significantly influence fate decisions. Indeed, in addition to the composition of the surrounding medium, cells are highly sensitive to the properties of neighboring surfaces, including the spatial organization of anchored molecules and substrate mechanical and topographical properties. These properties should thus be included in models of cell behavior. It is also suggested that attempts at cell modeling could strongly benefit from two research lines: (i) trying to decipher the way cells encode the information they retrieve from environment analysis, and (ii) developing more standardized means of assessing the quality of proposed models, as was done in other research domains such as protein structure prediction.

The progress in titanium alloys used as biomedical implants: From the view of reactive oxygen species

Titanium and Titanium alloys are widely used as biomedical implants in oral and maxillofacial surgery, due to superior mechanical properties and biocompatibility. In specific clinical populations such as the elderly, diabetics and patients with metabolic diseases, the failure rate of medical metal implants is increased significantly, putting them at increased risk of revision surgery. Many studies show that the content of reactive oxygen species (ROS) in the microenvironment of bone tissue surrounding implant materials is increased in patients undergoing revision surgery. In addition, the size and shape of materials, the morphology, wettability, mechanical properties, and other properties play significant roles in the production of ROS. The accumulated ROS break the original balance of oxidation and anti-oxidation, resulting in host oxidative stress. It may accelerate implant degradation mainly by activating inflammatory cells. Peri-implantitis usually leads to a loss of bone mass around the implant, which tends to affect the long-term stability and longevity of implant. Therefore, a great deal of research is urgently needed to focus on developing antibacterial technologies. The addition of active elements to biomedical titanium and titanium alloys greatly reduce the risk of postoperative infection in patients. Besides, innovative technologies are developing new biomaterials surfaces conferring anti-infective properties that rely on the production of ROS. It can be considered that ROS may act as a messenger substance for the communication between the host and the implanted material, which run through the entire wound repair process and play a role that cannot be ignored. It is necessary to understand the interaction between oxidative stress and materials, the effects of oxidative stress products on osseointegration and implant life as well as ROS-induced bactericidal activity. This helps to facilitate the development of a new generation of well-biocompatible implant materials with ROS responsiveness, and ultimately prolong the lifespan of implants.

Topography-mediated immunomodulation in osseointegration; Ally or Enemy

Osteoimmunology is at full display during endosseous implant osseointegration. Bone formation, maintenance and resorption at the implant surface is a result of bidirectional and dynamic reciprocal communication between the bone and immune cells that extends beyond the well-defined osteoblast-osteoclast signaling. Implant surface topography informs adherent progenitor and immune cell function and their cross-talk to modulate the process of bone accrual. Integrating titanium surface engineering with the principles of immunology is utilized to harness the power of immune system to improve osseointegration in healthy and diseased microenvironments. This review summarizes current information regarding immune cell-titanium implant surface interactions and places these events in the context of surface-mediated immunomodulation and bone regeneration. A mechanistic approach is directed in demonstrating the central role of osteoimmunology in the process of osseointegration and exploring how regulation of immune cell function at the implant-bone interface may be used in future control of clinical therapies. The process of peri-implant bone loss is also informed by immunomodulation at the implant surface. How surface topography is exploited to prevent osteoclastogenesis is considered herein with respect to peri-implant inflammation, osteoclastic precursor-surface interactions, and the upstream/downstream effects of surface topography on immune and progenitor cell function.

Recent advances in nanomedicines for regulation of macrophages in wound healing

Macrophages are essential immune cells and play a major role in the immune response as pro-inflammatory or anti-inflammatory agents depending on their plasticity and functions. Infiltration and activation of macrophages are usually involved in wound healing. Herein, we first described macrophage polarization and their critical functions in wound healing process. It is addressed how macrophages collaborate with other immune cells in the wound microenvironment. Targeting macrophages by manipulating or re-educating macrophages in inflammation using nanomedicines is a novel and feasible strategy for wound management. We discussed the design and physicochemical properties of nanomaterials and their functions for macrophages activation and anti-inflammatory signaling during wound therapy. The mechanism of action of the strategies and appropriate examples are also summarized to highlight the pros and cons of those approaches. Finally, the potential of nanomedicines to modulate macrophage polarization for skin regeneration is discussed.

Autophagy Plays Multiple Roles in the Soft-Tissue Healing and Osseointegration in Dental Implant Surgery-A Narrative Review

Dental endo-osseous implants have become a widely used treatment for replacing missing teeth. Dental implants are placed into a surgically created osteotomy in alveolar bone, the healing of the soft tissue lesion and the osseointegration of the implant being key elements to long-term success. Autophagy is considered the major intracellular degradation system, playing important roles in various cellular processes involved in dental implant integration. The aim of this review is an exploration of autophagy roles in the main cell types involved in the healing and remodeling of soft tissue lesions and implant osseointegration, post-implant surgery. We have focused on the autophagy pathway in macrophages, endothelial cells; osteoclasts, osteoblasts; fibroblasts, myofibroblasts and keratinocytes. In macrophages, autophagy modulates innate and adaptive immune responses playing a key role in osteo-immunity. Autophagy induction in endothelial cells promotes apoptosis resistance, cell survival, and protection against oxidative stress damage. The autophagic machinery is also involved in transporting stromal vesicles containing mineralization-related factors to the extracellular matrix and regulating osteoblasts' functions. Alveolar bone remodeling is achieved by immune cells differentiation into osteoclasts; autophagy plays an important and active role in this process. Autophagy downregulation in fibroblasts induces apoptosis, leading to better wound healing by improving excessive deposition of extracellular matrix and inhibiting fibrosis progression. Autophagy seems to be a dual actor on the scene of dental implant surgery, imposing further research in order to completely reveal its positive features which may be essential for clinical efficacy.

The response of soft tissue cells to Ti implants is modulated by blood-implant interactions

Titanium-based dental implants have been highly optimized to enhance osseointegration, but little attention has been given to the soft tissue-implant interface, despite being a major contributor to long term implant stability. This is strongly linked to a lack of model systems that enable the reliable evaluation of soft tissue-implant interactions. Current in vitro platforms to assess these interactions are very simplistic, thus suffering from limited biological relevance and sensitivity to varying implant surface properties. The aim of this study was to investigate how blood-implant interactions affect downstream responses of different soft tissue cells to implants in vitro, thus taking into account not only the early events of blood coagulation upon implantation, but also the multicellular nature of soft tissue. For this, three surfaces (smooth and hydrophobic; rough and hydrophobic; rough and hydrophilic with nanostructures), which reflect a wide range of implant surface properties, were used to study blood-material interactions as well as cell-material interactions in the presence and absence of blood. Rough surfaces stimulated denser fibrin network formation compared to smooth surfaces and hydrophilicity accelerated the rate of blood coagulation compared to hydrophobic surfaces. In the absence of blood, smooth surfaces supported enhanced attachment of human gingival fibroblasts and keratinocytes, but limited changes in gene expression and cytokine production were observed between surfaces. In the presence of blood, rough surfaces supported enhanced fibroblast attachment and stimulated a stronger anti-inflammatory response from macrophage-like cells than smooth surfaces, but only smooth surfaces were capable of supporting long-term keratinocyte attachment and formation of a layer of epithelial cells. These findings indicate that surface properties not only govern blood-implant interactions, but that this can in turn also significantly modulate subsequent soft tissue cell-implant interactions.

Metallic Implants Used in Lumbar Interbody Fusion

Over the last decade, pedicle fixation systems have evolved and modifications in spinal fusion techniques have been developed to increase fusion rates and improve clinical outcomes after lumbar interbody fusion (LIF). Regarding materials used for screw and rod manufacturing, metals, especially titanium alloys, are the most popular resources. In the case of pedicle screws, that biomaterial can be also doped with hydroxyapatite, CaP, ECM, or tantalum. Other materials used for rod fabrication include cobalt-chromium alloys and nitinol (nickel-titanium alloy). In terms of mechanical properties, the ideal implant used in LIF should have high tensile and fatigue strength, Young's modulus similar to that of the bone, and should be 100% resistant to corrosion to avoid mechanical failures. On the other hand, a comprehensive understanding of cellular and molecular pathways is essential to identify preferable characteristics of implanted biomaterial to obtain fusion and avoid implant loosening. Implanted material elicits a biological response driven by immune cells at the site of insertion. These reactions are subdivided into innate (primary cellular response with no previous exposure) and adaptive (a specific type of reaction induced after earlier exposure to the antigen) and are responsible for wound healing, fusion, and also adverse reactions, i.e., hypersensitivity. The main purposes of this literature review are to summarize the physical and mechanical properties of metal alloys used for spinal instrumentation in LIF which include fatigue strength, Young's modulus, and corrosion resistance. Moreover, we also focused on describing biological response after their implantation into the human body. Our review paper is mainly focused on titanium, cobalt-chromium, nickel-titanium (nitinol), and stainless steel alloys.

3D printed magnesium-doped β-TCP gyroid scaffold with osteogenesis, angiogenesis, immunomodulation properties and bone regeneration capability in vivo

Bioceramics have been used in orthopedic surgery for several years. Magnesium (Mg) is an essential element in bone tissue and plays an important role in bone metabolism. Mg-doped bioceramics has attracted the attention of researchers recently. However, the optimal doping amount of Mg in β-TCP and the immunomodulatory property of Mg-doped β-TCP (Mg-TCP) have not been determined yet. In this study, β-TCP scaffolds doped with different contents of magnesium oxide (0 wt%, 1 wt%, 3 wt%, and 5 wt%) with gyroid structure were printed by digital light processing (DLP) method, and the physicochemical and biological functions were then investigated. Mg-doping improved the physicochemical properties of the β-TCP scaffolds. In vitro experiments confirmed that the doping of Mg in β-TCP scaffolds promoted the osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) and angiogenic differentiation of endothelial progenitor cells (EPCs), where the 5Mg-TCP has the optimal properties when using the "one cell type" method. It was also found that all Mg-TCP facilitated the polarization of RAW264.7 cells to the M2 phenotype, especially the 3Mg-TCP. However, 3Mg-TCP displayed the optimal osteogenic and angiogenic potential when using a "multiple cell type" method, which referred to culturing the BMSCs or EPCs in the macrophage-conditioned medium. Finally, the in vivo experiments were conducted and the results confirmed that the 3Mg-TCP scaffolds possessed the satisfying bone defect repair capability both after 6 and 12 weeks of implantation. This study suggests that 3Mg-TCP scaffolds provide the optimal biological performance and thus have the potential for clinical translation.

Gelatin-based Colloidal vs. Monolithic Gels to Regulate Macrophage-mediated Inflammatory Response

Unlike conventional monolithic hydrogels with covalent crosslinkage that are typically elastic, colloidal gels assembled by reversibly assembled particles as building blocks have shown fascinating viscoelastic properties. They follow a gel-sol transition upon yielding and recover to the initial state upon the release of the shear force (so-called shear-thinning and self-healing behavior); this makes them an ideal candidate as injectable and moldable biomaterials for tissue regeneration. The immune response provoked by the implantation of the colloidal gels with special viscoelastic and structural features is critical for the successful integration of the implants with the host tissues, which, however, remains little explored. Since macrophages are known as the primary immune cells in determining the inflammatory response against the implants, we herein investigated in vitro macrophage polarization and in vivo inflammatory response induced by gelatin-based colloidal gels as compared to monolithic gels. Specifically, self-healing colloidal gels composed of pure gelatin nanoparticles, or methacrylate gelatin (GelMA) nanoparticles to allow secondary covalent crosslinkage were compared with GelMA bulk hydrogels. We demonstrated that hydrogel's elasticity plays a more dominant role rather than the structural feature in determining in vitro macrophage polarization evidenced by the stiffer gels inducing pro-inflammation M2 macrophage phenotype as compared to soft gels. However, subcutaneous implantation revealed a significantly alleviated immune response characterized by less fibrous capsule formation for the colloidal gels as compared to bulk gels of similar matrix elasticity. We speculated this can be related to the improved permeability of the colloidal gels for cell penetration, thereby leading to less fibrosis. In general, this study provided in-depth insight into the biophysical regulator of hydrogel materials on macrophage behavior and related inflammatory response, which can further direct future implant design and predict biomaterial-host interactions for immunotherapy and regenerative medicine.

Promotion of trained innate immunity by nanoparticles

The dogma that immunological memory is an exclusive trait of adaptive immunity has been recently challenged by studies showing that priming of innate cells can also result in modified long-term responsiveness to secondary stimuli, once the cells have returned to a non-activated state. This phenomenon is known as 'innate immune memory', 'trained immunity' or 'innate training'. While the main known triggers of trained immunity are microbial-derived molecules such as β-glucan, endogenous particles such as oxidized low-density lipoprotein and monosodium urate crystals can also induce trained phenotypes in innate cells. Whether exogenous particles can induce trained immunity has been overlooked. Our exposure to particulates has dramatically increased in recent decades as a result of the broad medical use of particle-based drug carriers, theragnostics, adjuvants, prosthetics and an increase in environmental pollution. We recently showed that pristine graphene can induce trained immunity in macrophages, enhancing their inflammatory response to TLR agonists, proving that exogenous nanomaterials can affect the long-term response of innate cells. The consequences of trained immunity can be beneficial, for instance, enhancing protection against unrelated pathogens; however, they can also be deleterious if they enhance inflammatory disorders. Therefore, studying the ability of particulates and biomaterials to induce innate trained phenotypes in cells is warranted. Here we analyse the mechanisms whereby particles can induce trained immunity and discuss how physicochemical characteristics of particulates could influence the induction of innate memory. We review the implications of trained immunity in the context of particulate adjuvants, nanocarriers and nanovaccines and their potential applications in medicine. Finally, we reflect on the unanswered questions and the future of the field.

Lipidome profiling with Raman microspectroscopy identifies macrophage response to surface topographies of implant materials

Biomaterial characteristics such as surface topographies have been shown to modulate macrophage phenotypes. The standard methodologies to measure macrophage response to biomaterials are marker-based and invasive. Raman microspectroscopy (RM) is a marker-independent, noninvasive technology that allows the analysis of living cells without the need for staining or processing. In the present study, we analyzed human monocyte-derived macrophages (MDMs) using RM, revealing that macrophage activation by lipopolysaccharides (LPS), interferons (IFN), or cytokines can be identified by lipid composition, which significantly differs in M0 (resting), M1 (IFN-γ/LPS), M2a (IL-4/IL-13), and M2c (IL-10) MDMs. To identify the impact of a biomaterial on MDM phenotype and polarization, we cultured macrophages on titanium disks with varying surface topographies and analyzed the adherent MDMs with RM. We detected surface topography-induced changes in MDM biochemistry and lipid composition that were not shown by less sensitive standard methods such as cytokine expression or surface antigen analysis. Our data suggest that RM may enable a more precise classification of macrophage activation and biomaterial-macrophage interaction.

Changes in Spectral Fluorescence Properties of a Near-Infrared Photosensitizer in a Nanoform as a Coating of an Optical Fiber Neuroport

In this work, we tested a new approach to assess the presence of inflammatory process in the implant area using spectral methods and the technique of fiber fluorescence analysis of photosensitizers in nanoform. First of all, the spectral characteristics of the photosensitizer when interacting with the porous surface of the implant, based on hydroxyapatite under in vitro and in vivo conditions, were determined. Thus, it was shown that spectral characteristics of photosensitizers can be used for judgement on the process of inflammation in the implant area and thus on the local presence of the immunocompetent cells. The analysis was performed at a sufficient depth in the biotissue by using the near-infrared spectral region, as well as two different methods: fiber-based laser spectroscopy and fiber-optic neuroscopy, which served to monitor the process and regular fluorescence diagnosis of the studied area. Fluorescence spectroscopic analysis was performed on experimental animals in vivo, i.e., under conditions of active immune system intervention, as well as on cell cultures in vitro in order to judge the role of the immune system in the interaction with the implant in comparison. Thus, the aim of the study was to determine the relationship between the fluorescence signal of nanophotosensitizers in the near infrared spectral region and its parameters with the level of inflammation and the type of surface with which the photosensitizer interacts in the implant area. Thus, fiber-optic control opens up new approaches for further diagnosis and therapy in the implant area, making immune cells a prime target for advanced therapies.

Fitting pieces into the puzzle: The impact of titanium-based dental implant surface modifications on bacterial accumulation and polymicrobial infections

Polymicrobial infection is the main cause of dental implant failure. Although numerous studies have reported the ability of titanium (Ti) surface modifications to inhibit microbial adhesion and biofilm accumulation, the majority of solutions for the utilization of Ti antibacterial surfaces have been testedin in vitro and animal models, with only a few developed surfaces progressing into clinical research. Motivated by this huge gap, we critically reviewed the scientific literature on the existing antibacterial Ti surfaces to help understand these surfaces' impact on the "puzzle" of undesirable dental implant-related infections. This manuscript comprises three main sections: (i) a narrative review on topics related to oral biofilm formation, bacterial-implant surface interactions, and on how implant-surface modifications can influence microbial accumulation; (ii) a critical evidence-based review to summarize pre-clinical and clinical studies in an attempt to "fit pieces into the puzzle" to unveil the best way to reduce microbial loads and control polymicrobial infection around dental implants showed by the current in vivo evidence; and (iii) discussion and recommendations for future research testing emerging antibacterial implant surfaces, connecting basic science and the requirements for future clinical translation. The findings of the present review suggest no consensus regarding the best available Ti surface to reduce bacterial colonization on dental implants. Smart release or on-demand activation surface coatings are a "new piece of the puzzle", which may be the most effective alternative for reducing microbial colonization on Ti surfaces, and future studies should focus on these technologies.

Electrophoretic deposition of silk fibroin coatings with pre-defined architecture to facilitate precise control over drug delivery

The therapeutic precision and clinical applicability of drug-eluting coatings can be substantially improved by facilitating tunable drug delivery. However, the design of coatings which allows for precise control over drug release kinetics is still a major challenge. Here, a double-layered silk fibroin (SF) coating system was constructed by sequential electrophoretic deposition. A mixture of dissolved Bombyx mori SF (bmSF) molecules and pre-made bmSF nanospheres at different ratios was deposited as under-layer. Subsequently, this underlayer was covered by a top-layer comprising Antheraea pernyi SF (apSF) molecules (rich in arginylglycylaspartic acid, RGD) to improve the cellular response of the resulting double-layered coatings. Additionally, model drug doxycycline was either pre-mixed with dissolved bmSF molecules or pre-loaded into pre-made bmSF nanospheres at the same amount before their mixing and deposition. The thickness and nanosphere content of the under-layer architecture were proportional to the deposition time and nanosphere concentration in precursor mixtures, respectively. The surface topography, wettability, degradation rate and adhesion strength were comparable within the double-layered coating system. As expected, RGD-rich apSF top-layer improved cell adhesion, spreading and proliferation compared with bmSF top-layer. Furthermore, the amount and duration of drug release increased linearly with increasing nanosphere concentration at fixed deposition time, whereas drug release amount increased linearly with increasing deposition time. These results indicate that the dosage and kinetics of loaded drugs can be quantitatively tailored by altering nanosphere concentration and deposition time as main processing parameters. Overall, this study illustrates the strong potential of pre-defining coating architecture to facilitate control over drug delivery.

Control of innate immune response by biomaterial surface topography, energy, and stiffness

As the focus of implantable biomaterials has shifted from bioinert implants to bioactive designs, recent research has highlighted the complex interactions between cell physiologic systems and material properties, particularly physical cues. From the cells known to interact with implanted biomaterials, the response of the immune system has been a critical target of study recently. Here, we review studies characterizing the response of innate immune cells to various material cues, particularly of those at the surface of implanted materials.The innate immune system consists of cell types with various roles in inflammation. Neutrophils and macrophages serve both phagocytic and signaling roles, especially early in the inflammatory phase of biomaterial implantation. These cell types ultimately dictate the outcome of implants as chronic inflammation, fibrosis, or integration. Other cell types like dendritic cells, mast cells, natural killer cells, and innate lymphoid cells may also serve an immunomodulatory role in the biomaterial context. This review highlights recent advances in our understanding of the role of innate immunity in the response to implantable biomaterials as well as key mechanobiological findings in innate immune cells underpinning these advances. STATEMENT OF SIGNIFICANCE: This review highlights recent advances in the understanding of the role of innate immunity in the response to implantable biomaterials, especially in neutrophils and macrophages, as well as key mechanobiological findings in innate immune cells underpinning these advances. Here we discuss how physicochemical properties of biomaterials control innate immune cell behavior.

Non-union bone fractures

The human skeleton has remarkable regenerative properties, being one of the few structures in the body that can heal by recreating its normal cellular composition, orientation and mechanical strength. When the healing process of a fractured bone fails owing to inadequate immobilization, failed surgical intervention, insufficient biological response or infection, the outcome after a prolonged period of no healing is defined as non-union. Non-union represents a chronic medical condition not only affecting function but also potentially impacting the individual's psychosocial and economic well-being. This Primer provides the reader with an in-depth understanding of our contemporary knowledge regarding the important features to be considered when faced with non-union. The normal mechanisms involved in bone healing and the factors that disrupt the normal signalling mechanisms are addressed. Epidemiological considerations and advances in the diagnosis and surgical therapy of non-union are highlighted and the need for greater efforts in basic, translational and clinical research are identified.

Implant Fibrosis and the Underappreciated Role of Myofibroblasts in the Foreign Body Reaction

Body implants and implantable medical devices have dramatically improved and prolonged the life of countless patients. However, our body repair mechanisms have evolved to isolate, reject, or destroy any object that is recognized as foreign to the organism and inevitably mounts a foreign body reaction (FBR). Depending on its severity and chronicity, the FBR can impair implant performance or create severe clinical complications that will require surgical removal and/or replacement of the faulty device. The number of review articles discussing the FBR seems to be proportional to the number of different implant materials and clinical applications and one wonders, what else is there to tell? We will here take the position of a fibrosis researcher (which, coincidentally, we are) to elaborate similarities and differences between the FBR, normal wound healing, and chronic healing conditions that result in the development of peri-implant fibrosis. After giving credit to macrophages in the inflammatory phase of the FBR, we will mainly focus on the activation of fibroblastic cells into matrix-producing and highly contractile myofibroblasts. While fibrosis has been discussed to be a consequence of the disturbed and chronic inflammatory milieu in the FBR, direct activation of myofibroblasts at the implant surface is less commonly considered. Thus, we will provide a perspective how physical properties of the implant surface control myofibroblast actions and accumulation of stiff scar tissue. Because formation of scar tissue at the surface and around implant materials is a major reason for device failure and extraction surgeries, providing implant surfaces with myofibroblast-suppressing features is a first step to enhance implant acceptance and functional lifetime. Alternative therapeutic targets are elements of the myofibroblast mechanotransduction and contractile machinery and we will end with a brief overview on such targets that are considered for the treatment of other organ fibroses.